Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-07-30
2001-10-23
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S480000, C428S500000, C162S157200, C162S162000, C162S164100, C162S164700, C162S185000
Reexamination Certificate
active
06306493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to laser-markable paper and board products which include micronized polymers as absorber material and material for carbonization.
2. Description of the Background Art
The placing of distinguishing marks on products is becoming increasingly important in almost all sectors of industry. For example, it is frequently necessary to apply production dates, expiry dates, bar codes, company logos, serial numbers, etc. At the present, these markings are predominantly executed using conventional techniques, such as printing, embossing, stamping and labeling. However, the importance of non-contact, high-speed and flexible marking using lasers is increasing. This laser marking technique makes it possible to apply graphic inscriptions, for example bar codes, at high speed even to a non-planar surface.
In printed products for the packaging sector (folding cartons, labels, etc.), there has been an increased requirement that direct laser marking, coding and inscription of the paper and board products be made possible, without the printing-on of additional fields.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide laser-markable paper products which, when treated with laser light, make it possible to achieve a marking which has good legibility and crisp edges.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
Ordinarily, paper is difficult or impossible to mark with a laser, because its layer thickness is low. To make the paper capable of laser inscription, it is necessary to incorporate appropriate absorbers which carbonize at high temperatures into the paper. The absorber material should have a very pale neutral intrinsic color, and/or have the properties of the paper product to be marked, and at the same time required to be only in small amounts.
Surprisingly, it has now been determined that if micronized polymers composed of linear aromatic polyesters and/or of linear polyarylenes having a particle size of from 0.1 to 100 &mgr;m are incorporated as absorber material directly into the body and/or coating of the paper, the markings obtained on paper and board products would have high contrast, crisp edges and good legibility.
In view of the above, a preferred embodiment of the invention, therefore, provides laser-markable paper and board products which include micronized polymers composed of linear aromatic polyesters and/or of linear polyarylenes having a particle size of from 0.1 to 100 &mgr;m as absorber material and material for carbonization.
In a further preferred embodiment, adding the micronized polymers in concentrations of from 0.1 to 10% by weight based on the body of the paper, preferably from 1 to 5% by weight and in particular from 1 to 2% by weight, achieves high contrast in the laser marking. However, the concentration of the absorber in the body of the paper depends on the type of body of the paper and on the thickness of the paper and the energy density of the laser used. The relatively low proportion of absorber material neither alters the paper product significantly nor has any effect on its processability.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The crispness of the edges of the marking is determined in particular by the particle size of the micronized polymers applied to paper products. The polymers preferably have particle sizes in the range from 0.1 to 50 &mgr;m, in particular from 0.1 to 15 &mgr;m. Suitable absorber materials are, in particular, from the class of linear aromatic polyesters, the polycarbonates (PC), polyalkylene terephthalates (PTP), the poly(ether)esters and polyarylates. Particularly preferable polymers from the class of linear polyarylenes are the polyphenylene ethers (PPO and PPE), polyaryl ether ketones (PEK and PEEK), polyanilines, polyphenylene sulfides (PPS) and polysulfones (PSU, PES and PPSU).
It is also possible to use a combination of a mixture of different micronized polymers in any of the possible mixing ratios as absorber material and material for carbonization.
During the marking, the absorption achieved must not be so strong that the paper bums through leaving a black speck and/or a hole on the paper. The absorption of the laser radiation and the interaction with the absorber depends on many factors, inter alia, on the paper used. On the absorber and on the laser wavelength used. High-energy radiation is preferably used for the marking, generally in the wavelength range from 150 to 1500 nm, preferably from 150 to 1100 nm.
Example of the types of lasers used are CO
2
lasers (10,600 nm, Nd:YAG lasers (1067 or 532 nm) and pulsed UV lasers (excimer lasers).
The use of Nd:YAG lasers (1064 or 532 nm) or CO
2
lasers (10,600 nm) is particularly preferred. The energy densities of the lasers used are generally in the range from 0.3 mJ/cm
2
to 50 J/cm
2
, preferably from 0.5 mJ/cm
2
to 20 J/cm
2
and particularly preferably from 0.3 mJ/cm
2
to 10 J/cm
2
.
When pulsed lasers are used, the pulse frequency is generally in the range from 0.1 to 10,000 Hz, preferably from 0.5 to 5000 Hz and in particular from 1 to 1000 Hz, and the pulse lengths (duration of the individual pulse) are in the range from 0.1 to 1000 ns, preferably from 0.1 to 500 ns and particularly preferably from 1 to 100 ns.
Depending on the energy density of the laser used and on the pulse lengths and the type of paper product irradiated, the number of pulses required to achieve good inscriptions is generally from 1 to 20,000, preferably from 1 to 5000 and in particular from 1 to 3000.
With the aid of a laser, the novel process of laser marking for producing inscriptions with crisp edges and high contrast on any laser-markable paper or board product is possible. The inscription with the laser is brought about by placing the specimen in the path of a laser beam, preferably of a CO
2
or Nd:YAG laser. Inscription with an excimer laser is also possible. However, the desired results may also be achieved with other conventional types of laser which have a wavelength in the high absorption range of the absorber used. The shade and depth of color obtained are determined by the laser parameters, such as the time and power of irradiation. The power of the laser used depends on the individual application, and can easily be determined in a given case by the person skilled in the art.
Paper and board products, in particular for the packaging market sector, are generally composed of from 70 to 100% of natural and synthetic fibers, and from 20 to 30% of fillers and sizes, which form the middle layer of the paper and board products. These are useful for the invention.
A coating composition consisting of pigments for white coloration, binders and additives can be applied in one to three uniform applications onto raw paper to achieve a sealed, smooth surface for the printing and further processing. The coated papers are calendered matt or gloss and are produced coated on one or both sides.
The paddle stirrers and shapes of vessels used in the paper industry are suitable for incorporating the absorber materials into the body of the paper. The absorber material can be stirred in during the production of the paper stock at any stage of the paper making process before the paper machine is fed, or the absorber material may also be introduced into the coating composition.
Paper generally consists of mechanical and/or chemical pulp and, if desired, synthetic fibers and auxiliaries, such as fillers, binders for sizing, retention aids, optical brighteners and dyes. The absorber can be incorporated into the body of the paper in various ways. The absorber material can, for example, be mixed with the chemical and/or mechanical pulp in dry form. Alternatively, the absorber can be admixed with fibrous stock made from chemical and/or mechanical pulp. A homogeneous distribution of the absorber material is likewise achieved if the absorber material is added to the individual c
Merck Patent Gesellschaft
Millen White Zelano & Branigan P.C.
Paulraj Christopher G.
Thibodeau Paul
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